Method and apparatus for transmitting a coded video signal

ABSTRACT

A method and apparatus for transmitting a digitally encoded video image in real time via a data network wherein the video image is digitally encoded using a compression algorithm having a variable bit rate, e.g., JPEG2K, to provide an encoded data stream, the encoded data stream is fed into a buffer of known size, and the data is read from the buffer via a streamer with a controllable bit rate to provide a bit stream at a desired stream bit rate for transmission via the network. The bit rate of the encoded data stream from the encoder is monitored by a predictor and predicts a future bit rate of the encoded data stream; and, the bit rate of at least one of the encoder and the streamer is adjusted to provide the desired streaming bit rate.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for transmittinga coded video signal in real time via a data network. More particularly,the present invention relates to a method and apparatus for transmittingan encoded digital video signal in real time via a data network whereinthe encoding of the video image involves using a compression algorithmhaving a variable mid-rate to provide the digitally encoded data stream.

Since the mid-'90s, JPEG (Joint Photographic Export Group) is a standardthat has been very widely used in the compression of digital stillimages. However, and more recently, the study of wavelets, particularlywavelet transformers, has led to a new compression method that is calledJPEG 2000 or JPEG2K and variations thereof. Unlike the original JPEGalgorithm, the JPEG 2000 or JPEG2K algorithm can be applied to bothstill images and to motion video.

JPEG2K allows for up to a 200-1 compression ratio with very littleappreciable degradation in image quality, and has a lossy and losslessversion of the image compression. The image compression and theimpressive compression ratios are primarily obtained throughsegmentation of the video image or video frame into regions of interest(ROI's), and then applying an optimum family of wavelet transforms ontothe region. However, this impressive compression capacity comes as atrade-off of implementation complexity. This has generally led to mostreal-time JPEG2K systems currently available to be hardwire based.

The ROI-based scheme has resulted in the JPEG2K encoding to be based onquality levels as opposed to numerical encoding bit rate levels, asseen, for example, in MPEG 2, MPEG 4, etc schemes. As a result, in aJPEG 2K system, one decides among the different quality levels availableto configure the encoding process. For example, low, medium, and highcan form one particular quality characterization. These categories inturn are mapped to a numerical value of the difference between theoriginal and the JPEG2K reconstituted frame. In order to map the low,medium and high levels to the error, a metric such as Mean-Square-Error(MSE) can and often is used.

The quality-based encoding process used in JPEG2K leads to a variablebit rate encoding system. That is, the bit rate is dependent on theimage or video content. For example, a scene with motion would produce alarger encoding bit rate than a scene with no motion for a given qualitylevel. In the practical high-definition (HD) based JPEG2K systems, it iscommon to see the instantaneous coding rate vary from 2.4 Mbps for astill scene, to 64 Mbps for a complex scene. However, this variable bitrate poses a challenge in a streaming environment of a data network,e.g., the internet streaming environment. To accommodate the dynamicnature of the network bandwidth, most streaming systems use a constantbit rate streaming mechanism. The constant bit rate is chosen to providethe maximum likelihood of error-free transmission within the network.Streaming protocols such as RSVP are used to reserve bandwidth with suchconstant bandwidth streaming channels. In the above environments, thevariable bit rate of JPEG2K poses a problem.

It is the general object of the present invention to control theencoding bit rate and/or the streaming bit rate so as to be better ableto control the streaming bit rate within the confines of the streamingenvironment, while at the same time permitting maximum quality oftransmission.

SUMMARY OF THE INVENTION

The above object generally is achieved according to the presentinvention by a method of transmitting a coded video image in real timevia a data network that comprises digitally encoding a video image usinga compression algorithm having a variable bit rate to provide an encodeddata stream; feeding the encoded data stream into a buffer of knownsize; reading data from the buffer via a streamer with a controllablebit rate to provide a bit stream at a desired stream bit rate fortransmission via the network; monitoring the bit rate of the encodeddata stream from the encoder and predicting a future bit rate of theencoded data stream; and, adjusting the bit rate of at least one of theencoder and the streamer to provide the desired streaming bit rate.

According to features of the present invention, the prediction iscarried out using a prediction model that maps bit rate vs. time basedon a second or higher order polynomial to ensure smoothness of the bitrate vs. time curve, and the encoding algorithm is a JPEG2K algorithm.

According to a further feature of the invention the relationship betweenthe encoding and streaming bit rates is defined as follows:

With this relationship, the size of the buffer can be enlarged by anamount equal to the momentary encoded bit rate minus the momentarystreaming bit rate when the streaming bit rate is set to a maximum valuesuch that further increase would result in a buffer overflow condition.

According to one embodiment of the basic invention, the method furtherincludes defining a set of strip-wise constant bit rate streaminglevels; and the bit rate is adjusted by raising and lowering thestreaming bit rate level proportionately to an increase or decrease ofthe predicted encoded bit rate level, using the set of step-wisestreaming levels.

According to a further embodiment of the basic invention, the methodfurther includes providing the encoding algorithm with a defined set ofquality levels proportional to the encoding bit rate; and the bit rateis adjusted by decreasing the encoding quality level, and thus theencoding bit rate, if the predicted encoding bit rate is greater than amaximum streaming bit rate level. Additionally, the bit rate may beadjusting by increasing the encoding quality level, and thus theencoding bit rate, if the predicted encoding bit rate plus a giventhreshold value is less than the maximum streaming bit rate level, wherethe threshold value is an empirical number based on an analysis ofrepresentative video streams.

According to a further aspect of the invention, an apparatus forcarrying out the method according to the invention basically comprises:a video encoder for encoding a video image using a compression algorithmhaving a variable bit rate to provide an encoded data stream; a bufferof known size connected to receive the encoded data stream; a streamerwith a controllable bit rate connected to the buffer to read data fromthe buffer and to provide a bit stream at a desired stream bit rate fortransmission via the network; a predictor monitoring the bit rate of theencoded data stream from the encoder and predicting a future bit rate ofthe encoded data stream; and, a control arrangement adjusting the bitrate of at least one of the encoder and the streamer to provide thedesired streaming bit rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a basic block circuit diagram illustrating the streamer modelas well as the control thereof.

FIG. 2 illustrates a representative prediction curve of bit rate versustime for a predictor used according to the present invention.

FIG. 3 is a curve showing a set of stepwise constant bit rate streaminglevels defined according to the present invention.

FIG. 4 is a flow diagram illustrating the operation of the method andapparatus according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown the basic streamer model for thearrangement according to the invention for the transmission of theencoded video signal.

As shown, the video image is sent to a video encoder 10, which digitallyencodes the video image using an algorithm having a variable bit rate,for example, a JPEG 2K encoder, and has a set of defined quality levels,for example, super low, low, medium, high, super high. These qualitylevels will be proportional to the encoding rate. The output from thevideo encoder 10 is, as shown, fed to a buffer 12 which is of knownsize, and which operates in a conventional manner as a first-in, firstout buffer, and from the buffer 12 to a streamer 14, which extracts thedata from the buffer 12 and produces a data stream at a streamer bitrate dictated by the network, e.g., the internet. The output of thestreamer 14 is then fed as the stream of data to the network at thestreamer bit rate.

According to the invention, a predictor 16 is provided to monitor theencoded bit stream produced by video encoder 10 and to predict thefuture bit rate of the bit stream. The predictor is based on theknowledge that motion content is typically smooth over time for mostnatural scenes. That is, there is a high content-based correlation intime between adjacent frames and this is a fundamental property that isexploited by all compression schemes. The exceptions to this rule areinstances of scene changes and scene cuts, etc. However, these instancescan be regarded as statistical outliers and disregarded. In general, thepredictor 16 is based on a prediction model that maps bit rate versustime for the encoded video signal. The prediction model should be basedon a second or higher order polynomial that ensures the smoothness ofthe bit rate curve, and such a curve is shown in FIG. 2. As can easilybe seen, at higher complexities of the scene, the bit rate is muchhigher and the bit rate is at a minimum for the low to very lowcomplexity scene.

The outpoint of the predictor is sent to a microprocessor 18, which,based on the output of the predictor 16, controls the bit rate for oneor both of the video encoder 10 and the streamer 14.

According to one feature of the invention, the variable bit rate of theencoder 10 is controlled such that its maximum encoding bit rate doesnot exceed the maximum allowable streaming bit rate provided by thestreamer 14. For this purpose, and for a given size of the buffer 12, aheuristic algorithm is used to control the bit rate of the encoder 10 asfollows.

As shown in FIG. 4, if the output of the predictor 16 indicates that thepredicted encoded bit rate is less than the maximum bit rate streaminglevel (S20), nothing is done (S22). That is, no further control actionof the bit rate of the encoder 16 is carried out. Alternatively, if thepredicted encoded bit rate is not less than the maximum, then thequality level of the encoder 10 is decreased, for example, from minimumto low (S24). Moreover, if the predicted encoding bit rate plus somethreshold value is less than the maximum streaming bit rate level fromthe streamer 14 (S30), the quality level of the encoder 10 is increased,for example, from medium to high (S32). Alternatively, if the predictedencoder bit rate plus the threshold value is greater than the maximumstreaming bit rate level, then no change is made to the encoder bitrate. For this purpose, the threshold value will be an empirical numberbased on an analysis of representative video streams. As can beappreciated, as a result of this method, the quality of the encodedpicture being transmitted by the streamer can be improved.

According to a further embodiment or feature of the basic invention, astepwise constant bit rate streaming mechanism for a variable bit rateencoding system, for example, a JPEG2K encoding system, is defined andprovided as shown in FIG. 3. As with the prior embodiment, the output ofthe predictor 16 is utilized, but in this case is used to control thebit rate of the streamer 14 according to the stepwise bit rate curve ofFIG. 3. Moreover, the behavior of the streaming model of FIG. 1 isdefined according to the following relationship:

a. encoding bit rate (n)=data input to buffer (n);

b. data in buffer (n)=data in buffer (n−1)+encoding bit rate (n)

-   -   i. streaming bit rate (n);

c. encoding bit rate (n)=delta (t)+streaming bit rate (t), and

d. delta (t)=data in buffer (n)−data in buffer (n−1).

Therefore, for a buffer 12 of a given size, the streaming bit rate (n)must be controlled in a manner proportional to the encoder bit ratebased on the prediction, i.e., the predicted encoder bit rate. This canbe accomplished by making a decision to raise or lower the streaming bitrate level in accordance with the predicted encoder bit rate using thebit rate level curve of FIG. 3. That is, as shown in FIG. 4, a decisionis made in the microprocessor 18 of whether or not the predicted encoderbit rate corresponds to the current or present streaming bit rate level(S40), i.e., whether or not a change is required based on the definedbehavior of the streaming model. If in the affirmative, then nothing isdone for the present (S42). However, if the result of S40 is a negativeresponse, then a decision is made regarding whether an increase (oralternatively, a decrease is desired (S44). If an increase is desired,then the streaming bit rate level is step increased as needed, accordingto the curve of FIG. 4, to the step corresponding to the predictedencoder bit rate (S46). Alternatively, if a decrease in the streaminglevel is indicated, then the streaming bit rate level is decreased tothe corresponding step level as defined by the curve of FIG. 4. (S48).Moreover, in the case where the streaming bit rate cannot be increasedfurther, i.e., if set to a maximum for the data network, the buffer sizecan be enlarged by the microprocessor 18 by a size or amount equal tothe encoder bit rate (n) minus (−) the streamed bit rate (n) in order toavoid a buffer overflow condition.

It should be noted that although each of the different methods can beutilized individually, they can, if desired, also be usedsimultaneously. Moreover, while the method according to the inventioncan be implemented by hardware, it is best implemented bysoftware/firmware, which allows for the maximum degree of flexibility.

Finally, it should be noted that while the invention has been describedfor an encoder utilizing a JPEG2000 or JPEG2K compression algorithm, theinvention is applicable to and can be used with any digital encoderhaving a compression algorithm with a variable bit rate.

It will be appreciated that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

1. A method of transmitting a coded video image in real time via a datanetwork comprising: encoding a video image using a compression algorithmhaving a variable bit rate to provide an encoded data stream; feedingthe encoded data stream into a buffer of known size; reading data fromthe buffer via a streamer with a controllable bit rate to provide a bitstream at a desired stream bit rate for transmission via the network;monitoring the bit rate of the encoded data stream from the encoder andpredicting a future bit rate of the encoded data stream; and, adjustingthe bit rate of at least one of the encoder and the streamer to providethe desired streaming bit rate.
 2. The method according to claim 1,wherein the prediction is carried out using a prediction model that mapsbit rate vs. time based on a second or higher order polynomial to ensuresmoothness of the bit rate vs. time curve.
 3. The method according toclaim 1, wherein the encoding algorithm is a JPEG2k algorithm.
 4. Themethod according to claim 1, further including defining a set ofstrip-wise constant bit rate streaming levels; and wherein the adjustingincludes raising and lowering the streaming bit rate proportionately toan increase or decrease of the predicted encoded bit rate level, usingthe set of step-wise streaming levels.
 5. The method according to claim4 further comprising enlarging the buffer size by a amount equal to themomentary encoded bit rate minus the momentary streaming bit rate whenthe streaming bit rate is set to a maximum value such that furtherincrease would result in a buffer overflow condition.
 6. The methodaccording to claim 4 further including defining a relationship betweenthe encoding and streaming bit rate as follows: Encoding bit rate(n)=data input to buffer (n); Data in buffer (n)=data in buffer(n−1)+encoding bit rate (n)−streaming bit rate (n); Encoding bit rate(n)=delta (n)+streaming bit rate (n); and delta (n)=data in buffer(n)−data in buffer (n−1)
 7. The method according to claim 1, furtherincluding providing the encoding algorithm with a defined set of qualitylevels proportional to the encoding bit rate; and wherein the adjustingincludes decreasing the encoding quality level, and thus the encodingbit rate, if the predicted encoding bit rate is greater than a maximumstreaming bit rate level.
 8. The method according to claim 7, whereinthe adjusting further includes increasing the encoding quality level,and thus the encoding bit rate, if the predicted encoding bit rate plusa given threshold value is less than the maximum streaming bit ratelevel, where the threshold value is an empirical number based on ananalysis of representative video streams.
 9. The method according toclaim 1, further including providing the encoding algorithm with adefined set of quality levels proportional to the encoding bit rate; andwherein the adjusting includes increasing the encoding quality level,and thus the encoding bit rate, if the predicted encoding bit rate plusa given threshold value is less than the maximum streaming bit ratelevel, where the threshold value is an empirical number based on ananalysis of representational video streams.
 10. A method of transmittinga coded video signal in real time via a data network comprising:encoding a video signal using a compression algorithm, having a variablebit rate and a defined plurality of quality levels with correspondingdiffering bit rates, to provide an encoded data stream; feeding theencoded data stream to a buffer of known size; reading data from thebuffer via a streamer with a controllable bit rate to provide a bitstream at a desired streaming bit rate for transmission via the network.monitoring the bit rate (n) of the encoded data signal and predicting afuture bit rate (n+1) of the encoded data stream based on the bit rate(n); and, decreasing the encoding quality level, and thus the encodingbit rate, if the predicted encoding bit rate (n+1) is greater than amaximum permitted streaming bit rate.
 11. The method according to claim10, further including increasing the encoding quality level, and thusthe encoding bit rate, if the predicted encoding bit rate (n+1) plus athreshold value is greater than a maximum permitted streaming bit rate,where the threshold value is an empirically derived number based on ananalysis of representative video signal bit streams.
 12. The methodaccording to claim 10, wherein the prediction is carried out using aprediction model that maps bit rate vs. time based on a second or higherorder polynomial to insure smoothness of a bit rate vs. time curve. 13.The method according to claim 11, wherein the encoder algorithm is aJPEG2k algorithm.
 14. A method of transmitting a coded video signal inreal time via a data network comprising: encoding a video signal using acompression algorithm having a variable bit rate and a defined pluralityof quality levels with corresponding differing bit rates, to provide anencoded data stream; feeding the encoded data stream to a buffer ofknown size; reading data from the buffer via a streamer with acontrollable bit rate to provide a bit stream at a desired streaming bitrate for transmission via the network. monitoring the bit rate (n) ofthe encoded data signal and predicting a future bit rate (n+1) of theencoded data stream based on the bit rate (n); defining a set ofstep-wise constant bit rate streaming levels; and, increasing ordecreasing the step level of the streaming bit rate (n+1), and thus thestreaming bit rate, based on an increase or decrease, respectively, ofthe predicted encoding bit rate (n+1).
 15. The method according to claim14, enlarging the size of the buffer by a amount equal to the encodingbit rate (n) minus the streaming bit rate (n) when the streaming bitrate is at a maximum level such that further increase in the streamingbit rate would result in a buffer overflow condition.
 16. The methodaccording to claim 14, further including defining a relationship betweenthe encoding and streaming bit rates as follows: encoding bit rate(n)=data input to buffer (n); data in buffer (n)=data in buffer(n−1)+encoding bit rate (n)−streaming bit rate (n); encoding bit rate(n)=delta (t)+streaming bit rate (t), and delta (t)=data in buffer(n)−data in buffer (n−1).
 17. The method according to claim 14, whereinthe prediction is carried out using a prediction model that maps bitrate vs. time based on a second or higher order polynomial to insuresmoothness of a bit rate vs. time curve.
 18. The method according toclaim 14, wherein the encoder algorithm is a JPEG2k algorithm. 19.Apparatus for transmitting a coded video image in real time via a datanetwork comprising: a video encoder for encoding a video image using acompression algorithm having a variable bit rate to provide an encodeddata stream; a buffer of known size connected to receive the encodeddata stream; a streamer with a controllable bit rate connected to thebuffer to read data from the buffer and to provide a bit stream at adesired stream bit rate for transmission via the network; a predictormonitoring the bit rate of the encoded data stream from the encoder andpredicting a future bit rate of the encoded data stream; and, a controlarrangement adjusting the bit rate of at least one of the encoder andthe streamer to provide the desired streaming bit rate.
 20. Theapparatus according to claim 19, wherein the predictor uses a predictionmodel that maps bit rate vs. time based on a second or higher orderpolynomial to ensure smoothness of the bit rate vs. time curve.
 21. Theapparatus according to claim 19, wherein the encoder algorithm is aJPEG2k algorithm.
 22. The apparatus according to claim 19, wherein: aset of strip-wise constant bit rate streaming levels are defined for thestreamer; and the control arrangement raises and lowers the streamingbit rate proportionately to an increase or decrease of the predictedencoded bit rate level, using the set of step-wise streaming levels. 23.The apparatus according to claim 22 wherein the control arrangementenlarges the buffer size by a amount equal to the momentary encoded bitrate minus the momentary streaming bit rate when the streaming bit rateis set to a maximum value such that further increase would result in abuffer overflow condition.
 24. The apparatus according to claim 22wherein the control arrangement maintains the following definedrelationship between the encoding and streaming bit rates: Encoding bitrate (n)=data input to buffer (n); Data in buffer (n)=data in buffer(n−1)+encoding bit rate (n)−streaming bit rate (n); Encoding bit rate(n)=delta (n)+streaming bit rate (n); and delta (n)=data in buffer(n)−data in buffer (n−1)
 25. The apparatus according to claim 19,wherein: the encoding algorithm includes a defined set of quality levelsproportional to the encoding bit rate; and the control arrangementdecreases the encoding quality level and thus the encoding bit rate, ifthe predicted encoding bit rate is greater than a maximum streaming bitrate level.
 26. The apparatus according to claim 25, wherein: thecontrol arrangement increases the encoding quality level, and thus theencoding bit rate, if the predicted encoding bit rate plus a giventhreshold value is less than the maximum streaming bit rate level, wherethe threshold value is an empirical number based on an analysis ofrepresentative video streams.
 27. The apparatus according to claim 19,wherein the encoding algorithm includes a defined set of quality levelsproportional to the encoding bit rate; and the control arrangementincreases the encoding quality level, and thus the encoding bit rate, ifthe predicted encoding bit rate plus a given threshold value is lessthan the maximum streaming bit rate level, where the threshold value isan empirical number based on an analysis of representative videostreams.